Superabsorbent polymers (SAPs) are synthetic polymer materials having a capacity for absorbing 500 to 1000 times their own weight in moisture. Although developed for practical use in sanitary items such as disposable diapers for children, SAPs now find additional applications in a variety of fields including raw materials in soil conditioners for horticulture, water stopping agents for civil engineering and construction applications, sheets for raising seedlings, freshness preservatives for food distribution, goods for fomentation, and the like.
The absorption mechanism of SAPs is governed by interactions of various factors including the osmotic pressure attributed to a difference in the electric attraction shown by a charge of a polymer electrolyte, the affinity between water and the polymer electrolyte, the molecular expansion attributed to repulsive force between ions of polymer electrolyte, and the expansion restraint due to cross-link bonds. In other words, the absorbency of SAPs depends on the affinity and molecular expansion while the absorption rates are greatly influenced by the osmotic pressure of the water absorbent polymer itself.
Extensive research has been directed towards an improvement in the absorption rate of SAPs. For example, Korean Patent Application Unexamined Publication No. 2007-0012623 A discloses a particulate water absorbing agent in which contents of resin particulates are determined according to the size thereof. However, the absorbing agent still needs an improvement in both absorption rate and water permeability.